You didn't even mention the original federal gun control law. The National Firearms Act. It was for violations that act, not GCA '68 or any other "law", that folks were killed at Ruby Ridge (too short) and Waco (alleged machine guns). It's just as unconstitutional as the others. It's alos the only one to make it to the Supreme Court, in a cast which was sent back to the lower court for "further action", which could have been anything, from reinstatement of the charges, to further pleadings and evidence that a short barrelled shotgun did have militia/military usefulness. The machine gun provisions, the associtated tax, and registry, have never been tested at the Supreme Court.
I agree 100% with you regarding the NFA. I didn't mention it because it affects less people, and most of what the BAT F'ers do is based on the GCA. That "sporting purposes" clause is the cause of more harm than virtually anything else.